MTB - Wheel Help Request

[mgm777]

The rear tire on my wife's 26 inch, shrader valve, MTB continually flats. When I disassemble the tire, I have noticed the shrader stem is cut, at the base, where the stem protrudes through the rim. I assume it is because the edges of the hole, on the rim, are sharp enough to cut the tube? I have attempted to smooth the edges of the rim hole with a round file, but apparently I did not do the job well enough, because it went flat again. Am I missing something? Any advice from collective will be appreciated. Thanks in advance.

[avalonracing]

The rear tire on my wife's 26 inch, shrader valve, MTB continually flats. When I disassemble the tire, I have noticed the shrader stem is cut, at the base, where the stem protrudes through the rim. I assume it is because the edges of the hole, on the rim, are sharp enough to cut the tube? I have attempted to smooth the edges of the rim hole with a round file, but apparently I did not do the job well enough, because it went flat again. Am I missing something? Any advice from collective will be appreciated. Thanks in advance.

I've had presta rims that do this. My solution was to take a small piece of Velox rim tape and punch a hole in it with a standard paper hole punch. It is big enough for the presta valve to just fit through but smaller than the rim hole. You could probably do something like this but with a bigger hole.

[Kirk Pacenti]

This: http://www.bicycletires.com/product/wheel-mfg-presta-stem-savers